Doctor Light

Kimiyo Hoshi was the supervising astronomer at an observatory in Japan, overseeing a group of male astronomers charting the unnatural effects of the Crisis on Infinite Earths. (She is also a scientist, as mentioned in Crisis on Infinite Earths #7 (October 1985), and a medical doctor, as shown in Justice League Annual #3 (1989) and Justice League America #55 (October 1991).)

Disgusted by the men's fear of the approaching antimatter cloud, she arrogantly tells them all off (including her own father), and orders them to leave, so she can study the phenomenon alone through her telescope.

Meanwhile, the Monitor, a being linked with all positive matter, senses his enemy, the Anti-Monitor, absorbing yet another positive-matter Earth with his antimatter cloud. In order to tip the scales for the heroes of the positive universe, the Monitor activates one last warrior.

He sends a devastating beam of energy from the star Vega to Earth, which strikes the observing Hoshi, leaving massive destruction in its wake. Granted the power of photonics and the name Doctor Light, Hoshi is assigned by the Monitor to guard one of the vibrational forks needed to save the Earth. Teen Titans member Starfire and Outsiders member Halo set out to destroy the machine. Since Doctor Light can't speak to them in English, she resorts to blasting them away from the machine. Superman is the first to communicate with her, given his knowledge of most of Earth's languages.

Once the Earth's heroes are brought aboard the Monitor's satellite, the Japanese-speaking Katana takes over as Kimiyo's translator.

Doctor Light, granted the ability to understand English, accompanies several heroes to the anti-matter universe to confront the Anti-Monitor. She and Superman soon discover the machines that the villain has deployed to destroy the remaining Earths. The Anti-Monitor ambushes the Man of Steel; Doctor Light defends Superman as best she can. Supergirl arrives, and sacrifices her life, allowing Doctor Light to carry the unconscious Superman to safety.

Seeing Supergirl's sacrifice makes Doctor Light realize how selfish she has been, and she resolves to change.

When Harbinger summons her to fight in the final battle, Doctor Light is ready. As the other heroes barrage the Anti-Monitor, she absorbs the energy of a gigantic star that he is using as a power source. Scoring the first fall of the Anti-Monitor during that battle, she blasts a gaping hole through him.